The present invention relates to glass compositions used in the production of colored glazings, particularly for motor vehicle sunroofs.
Now, more than ever before, automobile designers are incorporating into their designs glazings formed of colored glass which have both a functional purpose and an attractive appearance. This tendency is confirmed by the ever increasing glazed surface of new automobile models compared with older types.
As a result, the greenhouse effect is an important factor which must be taken into account in determining the air conditioning requirements for such automobiles. This is more particularly true in the case of cars equipped with glass sunroofs. In an attempt to reduce this greenhouse effect, numerous unsuccessful attempts have previously been made by those skilled in the art to produce colored glass compositions having the low light and energy transmission properties offered by the glasses of the present invention.
The present invention is directed to glass compositions which are highly colored, particularly grey-blue or green glasses, which are suitable for the applications described above. For a given thickness, these glasses have a very low total light transmission and total energy transmission.
According to the invention, these attributes are obtained with the use of a colored glass formulation comprising the following constituents in the weight proportions defined by the following limits:
wherein the total amount of the alkaline earth oxides ranges between 6 and 16% by weight and further wherein the total amount of alkali metal oxides is between 10 and 20% by weight. At least one of Al2O3, B203, MgO or K2O, each in an amount of up to 5% (0.05) by weight, therefore may be employed. The glass compositions of the invention also incorporate, as coloring agents:
The amount of CoO is preferably greater than about 0.02% by weight when the amount of Fe2O3 is less than about 2% by weight. Optionally, selenium and/or chromium oxide may also be added to the glass composition to provide additional coloration. The sum of CoO+selenium+Cr2O3 is preferably no greater than 0.24. The glass of the invention has a total light transmission factor under illuminant A (i.e., designated as xe2x80x9cTLAxe2x80x9d) less than or equal to about 20% and a total energy transmission factor (i.e., xe2x80x9cTExe2x80x9d) equal to or below approximately 12% at a xe2x80x9cstandardxe2x80x9d glass thickness of 3.85 mm.